And if I don't got enough in the tank, maybe I can just siphon enoughTo fill up this last can, man will I survive in this climate or what?

Eminem is comparing his energy to car fuel. So he’s saying that he will siphon which means get more energy or fuel from another source. He is thus wanting more energy to survive this contemporary “climate” a.k.a. the rap game and stay relevant.
Again with the evolution theme he skillfully plays in this song.

Eminem annexes a piece of wordplay to climate, he pronounces it so it sounds like climb it — effectively setting the allusion of conquering any obstacle in his field of vision.
The line can be seen as man will I survive in this? climb it or what? delivering the sense that there is only one option, which is to survive and overcome/climb it.